The vehicle power trains known from practice are usually realized in such a way that a driving torque generated by a driving motor can be guided, as needed, to the driving wheels via a gear device. In vehicles with several drivable vehicle axles, such as cars or trucks with all-wheel drive, the output of the driving motor is distributed in the power train of the vehicle to the individual vehicles axles and the different driving wheels of the vehicle axles.
The power distribution described above generally takes place via a transfer case or differential gear wherein longitudinal differential gears seen in the direction of travel are used for the longitudinal distribution of the driving power of the driving motor to several driven vehicle axles. So-called transverse differentials or balancing differentials are provided for a transverse distribution of the driving power to the driving wheels of a vehicle axle with reference to the direction of travel of a vehicle.
Conventional designs of differential gears are the bevel gear differentials, spur gear differentials with a planetary design or also worm gear differentials. Especially the aforementioned spur gear differentials are mostly used as longitudinal differentials because of the possibility of an asymmetrical torque distribution. Meanwhile the bevel gear differentials have become the standard for a transverse compensation in vehicles. Worm gear differentials are used for longitudinal distribution as well as for transverse distribution.
In these differential-controlled all-wheel drives or all-wheel systems known from the practice, the torque distribution to the front and rear axle occurs via a planetary gear differential or a bevel gear differential. The driving torque can be distributed as desired to the two driving axles or vehicle axles by selecting the gear ratio with the planetary gear differentials. The customary torque distributions between the front and rear axle are between 50%:50% and 33%:66%. In bevel gear differentials, the torque distribution is almost at 50%:50%. The torque distribution is ideal only for one point, the design point, due to the selection of a fixed torque ratio between the front and rear axle.
Consequently, the driving torque is not distributed in proportion to the axle load that corresponds to the present driving condition. If the traction reserves are to be utilized in their entirety when there is high slip, which is theoretically only possible with variable torque distribution between the front and rear axle; the longitudinal differential can be stopped or blocked. The vehicle performance is not negatively influenced by a continuously started locking effect caused by an increasing rotational speed difference, for example, via a viscous clutch and a permanent faulty gripping in the power train, such as can occur in positive locks, is prevented.
The previously described concepts, however, for the distribution of a driving torque of an input shaft between two drivable drive shafts have the disadvantage that they require a large installation space and, therefore, are difficult to integrate into the current gearbox plans.
It is, therefore, an objective of the invention to make a transfer case available having such a low requirement of installation space that the transfer case can be easily integrated in the existing gearbox plans and a torque distribution can be carried out by way of the transfer case, as needed, and dependent upon the operating condition between at least two drivable output shafts.
This objective is achieved with a transfer case in accordance with the features of patent claim 1.